Traditional engine starting mechanisms use an electric motor to drive the crankshaft to start the motor. The electric motor has a pinion gear driven by an output shaft of the motor. A ring gear is connected with a flex plate mounted to the engine crankshaft. When operating conditions warrant, the pinion gear is moved into meshing engagement with the ring gear so that the motor will drive the crankshaft. An actuator is typically used to move the pinion gear. The ring gear, and hence the engine crankshaft must be stationary, or moving at the same speed as the pinion gear, in order to bring the pinion gear into meshing engagement with the ring gear. Actuation of the pinion gear adds a time delay to starting of the engine, slowing response time. Additionally, if the gears are not synchronous when meshed, damage to the gears and/or noise will result.
Some recent starting mechanisms have utilized a constantly meshing pinion gear and ring gear, with a one-way clutch that engages to transmit torque from the starting motor to drive the crankshaft under some conditions, and overruns after the engine is started. The one-way clutch requires lubrication. Packaging and lubrication requirements of the one-way clutch have required modifications to the engine and resulted in added axial length to the powertrain.